1. Field of the Invention
The present invention relates to communication systems, for example mounted to motor vehicles, each of which has a transmitting device and a receiving device capable of transmitting and receiving communication data between the transmitting device and the receiving device through a communication network.
2. Description of the Related Art
There have been proposed various techniques for an adaptive cruise control system to be mounted to motor vehicles and to perform a high precision adaptive cruise control on the basis of high-accuracy current location information obtained by a real time kinetic global positioning system (RTK-GPS). A GPS receiver receives high resolution data detected by RTK-GPS which contain latitude and longitude information. The GPS receiver transmits the received high resolution data to each of electronic control units (ECU) through an in-vehicle communication network such as a local interconnect network on the basis of communication protocols. However, such high resolution data having high precision latitude and longitude information detected by RTK-GPS has a large data volume (or a large bit length), when compared with the data volume of data used in a conventional in-vehicle communication network. This causes a problem of the high resolution data exceeding a permissible data size of a data frame, which is a transmission unit, used by the data transmission of the in-vehicle communication system. In other words, it is difficult for the conventional communication system to transmit high resolution data containing latitude data and longitude data in a single transmission.
By the way, a patent document, Japanese patent laid open publication No. 2010-134562, discloses a technique for dividing original data as high resolution data obtained by a steering angle sensor into high order data and low order data, and transmitting different data frames which contain the high order data and the high order data, respectively. When receiving both the data frame containing the high order data and the data frame containing the low order data, a device combines them together in order to reconstruct the original data.
As previously described, it is difficult for the conventional techniques to transmit high resolution data in a single transmission. In general, there is a possibility of causing a transmission delay of data frames or one or more data frames being lost in a data communication of an in-vehicle communication system through a communication bus under a high communication load. In general, such an in-vehicle communication system uses CAN communication protocols.
When location information representing a current location of a motor vehicle is divided into high order data and low order data, and the divided data is transmitted through the communication bus, there is a possibility for a receiver not to receive one or more divided data due to a data transmission delay or loss of one or more data frames. In this case, because the receiver cannot receive correct data representing the current location information, i.e. receive insufficient data, the adaptive cruise control system performs the adaptive cruise control on the basis of the received insufficient amount of the current location data, and it becomes difficult to correctly and precisely perform the adaptive cruise control for the motor vehicle.